To link to the entire object, paste this link in email, IM or documentTo embed the entire object, paste this HTML in websiteTo link to this page, paste this link in email, IM or documentTo embed this page, paste this HTML in website

MAGNETIZATION STUDY OF TWO DIMENSIONAL HELIUM THREE
by
Lei Guo
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PHYSICS)
August 2010
Copyright 2010 Lei Guo

This dissertation discusses a magnetization study of a two dimensional Fermi system. Our group developed a SQUID NMR system to study the magnetization of two dimensional helium three on both GTA grafoil and ZYX Graphite substrates. Beneﬁting from SQUID technology, our NMR experiments were performed at very low applied magnetic ﬁeld thus avoid the masking of ordering by strong external ﬁeld.; Monolayer helium three ﬁlms adsorbed on crystalline graphite are considered a nearly ideal example of a two dimensional system of highly correlated fermions. By controlling the helium three areal density, adsorbed ﬁlms exhibit a wide range of structures with different temperature-dependent magnetic properties and heat capacities. Our recent experiments on two dimensional helium three adsorbed on ZYX graphite focused on the anti-ferromagnetic 4/7 phase and the ferromagnetic incommensurate solid state of a second helium three monolayer.; Ferromagnetic order was observed in two dimensional helium three ﬁlms on both Grafoil and highly oriented ZYX grade exfoliated graphite. The dipolar ﬁeld plays an important role in magnetic ordering in two dimensional spin systems. The dipole-dipole interaction leads to a frequency shift of the NMR absorption line. The resulting helium three NMR lineshape on Grafoil was a broad peak shifted towards lower frequency with a background from the randomly oriented regions extending to positive frequencies. Compared to Grafoil, ZYX graphite has a much greater structural coherence and is more highly oriented. When studying magnetism of helium three ﬁlms on ZYX substrate we found that the features we observed in our original Grafoil experiment were much more pronounced on ZYX graphite. In addition, we observed some multi-peak structure on the helium three NMR lineshape, which suggest a series of spin wave resonances.; We also studied the magnetic properties of the second layer of helium three ﬁlms on ZYX substrate at density around 4/7 phase. To eliminate the paramagnetic signal of the ﬁrst layer solid, we preplated a helium four layer on the ZYX that serves as a substrate for the helium three layer. In this region of density, the helium three ﬁlm acts as a quantum antiferromagnet with disordered ground state (Quantum Spin Liquid). Our experimental results are reported and similar work is reviewed.

MAGNETIZATION STUDY OF TWO DIMENSIONAL HELIUM THREE
by
Lei Guo
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PHYSICS)
August 2010
Copyright 2010 Lei Guo